As we all know, majority of my fellow Tamilians dont understand Hindi and even if they understand Hindi they find it extremely difficult to converse in Hindi. But I can be rest assured that while following a Tamil FM radio you hardly expect an all Hindi advertisement in Chennai and the moment it comes you mentally switch off and start looking for "songs" in other channels. Ordinarily the attention span of listeners for advertisements is very low in FM radio. I talk from my personal experience because as soon as the ads start coming my hand automatically goes in the process of tuning the other radio channels. Same with most of the people, I believe!!
But somebody who is authorising these advertisements within the Bank should really look for details like which cities are targeted, what should be language to be used, which radio stations are going to be used etc., They have a common Hindi advertisement which they play across all FM radio stations in India. One size fits all approach can't work here.